Measurement of the binding of deoxyguanosine to polycytidylic acid in which the cytosine residues have been modified by reaction with hyroxylamine and, in separate expriments, by reaction with nitrous acid. Measurement of the increase in binding of adenosine to these chemically modified polycytidylic acid samples. These experiments are designed to help reveal the mode of action of chemical mutagens. Measurement of the binding to polycytdylic acid and to polyuridylic acid of deoxyguanosine and adenine, respectively, which have been modified by alkylation with alkylating agents related to carcinogens and environmental mutagens. Measurement of energy transfer in systems where uracil and thymine are covalently linked at the 1- or 5-position with sidechains containing alpha-diketone chromophores. These experiments are designed to study transfer of triplet energy from the pyrimidine to the emitting chromophore. Preparation of uridine and thymine nucleoside phosphates with fluorescent labels in the 5-position, capable of being use in the enzymatic synthesis of homo-polynucleotides containing these labels.